1. Field of the Invention
The present invention relates to a measuring apparatus and a measuring method for measuring timing jitter in a data signal-under-measurement.
2. Description of Related Art
Conventionally, as a circuit for measuring timing jitter in a clock-signal-under-measurement, there has been known a circuit for measuring timing jitter by delaying the clock-signal-under-measurement by one period and by detecting a phase difference between the clock-signal-under-measurement and the delayed signal for example.
It has been also known to be able to measure jitter in a clock-signal -under-measurement by using a sampling oscilloscope and a digital oscilloscope.
However, although the conventional jitter measuring method is effective in measuring timing jitter in a pulse signal having a constant period such as the clock signal, it is unable to accurately measure timing jitter in a signal in which logic values appear irregularly such as a data signal.
For instance, while it is necessary to generate a triggering signal for measuring a phase of edges of the data-signal-under-measurement to measure timing jitter by using the sampling oscilloscope, the digital oscilloscope or the like, triggering signals of various timing have to be generated because the edges of the data signal are positioned irregularly. Therefore, timing jitter in the triggering signal itself becomes large, worsening the accuracy for measuring jitter in the data-signal-under-measurement.
Still more, because a high-precision circuit is required to generate triggering signals having less timing jitter, the measuring cost increases.
Therefore, it was unable to measure timing jitter in the data signal whose pattern is irregular at low cost and accurately by the conventional methods. Still more, neither method nor circuit for measuring jitter in a data signal in real-time has been invented yet.
Accordingly, it is an object of the invention to provide a jitter measuring apparatus and a jitter measuring method that are capable of solving the above-mentioned problems. This object may be achieved through the combination of features described in independent claims of the invention. Dependent claims thereof specify preferable embodiments of the invention.